1. Field of the Invention
The field of the invention is the employment of damping means to support structures for controlling vibration caused by external forces.
2. Description of the Prior Art
Laminated rubber supports for structures have been developed as illustrated in the Nikkei Architecture issue of Jul. 14, 1986, pp. 54-75. The conventional prior art laminated rubber support comprises vertically arrayed layers of solid rubber between which steel plates are interposed. The resultant lamination is sandwiched between upper and lower steel plates, which provide means for securing the lamination to upper and lower structures, such as a building superstructure and its foundation.
Conventionally, a solid laminated rubber support used in a structure's base isolation substructure deforms in proportion to its height. However, the diameter of the support must be reduced in order to reduce shearing stiffness. Therefore, two desirable physical properties of a solid prior art laminated rubber support, i.e., high deformation and low shearing moduli, have heretofore been difficult to obtain simultaneously.
As shown in prior art FIGS. 23 and 24, reduction of shearing modulus and increase in deformation modulus have been attempted by forming a hollow laminated rubber support. In so doing, however, the resistance of the support against buckling is reduced.
With reference to laminated rubber supports for uses other than as base isolation means, they have been known for use as springs in passive type vibration control devices and as spring elements or supporting devices in active type vibration control devices for controlling the vibration of a structure by applying a control force such as with oil pressure or electromagnetic force. In these vibration control devices, normally the natural period of the spring is synchronized with the natural period of a structure or it is set to be a period longer than the natural period of the structure (e.g., in cases where the vibration control device is used as a supporting device). A large stroke becomes necessary for getting a large seismic response control from a compact device. For example, an active-type vibration control device as disclosed in Japanese Pat. Laid-open No. 1-275866 is constructed with a weight which is hung from an upper steel frame and supported horizontally by pulleys and hanging members and in a way that the weight is capable of making relative movement against a building. The weight is connected to the building through a hydraulic cylinder. With direction from a control device, the weight pushes the cylinder through a hydraulic servo valve. The center of the cylinder is supported by a pin at the center of gravity of the weight and a piston of the cylinder is fixed to the building. However, there is a problem with this device in that the resulting movement in a vertical direction is also increased accordingly as the stroke becomes longer. In addition, when the natural period of a structure as a seismic response control object becomes longer, it becomes harder to use the laminated rubber supports having the period matching to such a device as described above. There is still a further problem, when vibrating the weight by means of the actuator as described, that the vibration due to the drive is transmitted to the building, resulting in the transmission of noise and undesirable vibration in the floor upon which the device is installed.